An auxiliary battery for a vehicle generally has a short service life of 2-3 years due to frequent charge and discharge thereof. On the other hand, an auxiliary battery of an eco-friendly vehicle has a low load during starting of the vehicle and is rapidly and accurately controllable by means of using a low voltage DC-DC converter (LDC), compared to the auxiliary battery of a typical engine vehicle. However, despite these structural merits, the auxiliary battery of the eco-friendly vehicle is managed similarly to the auxiliary battery of the engine vehicle in the absence of operational strategies of the auxiliary battery.
In other words, variable voltage control of the LDC is performed by setting a given control voltage at the request of a vehicle controller.
Referring to FIG. 1, the control voltage is configured as a low (fuel efficiency/discharge) mode, a medium (fuel efficiency/charge) mode, and a high (charge) mode. That is, generally, the low mode is applied during a discharge mode of the auxiliary battery in consideration of fuel efficiency, the medium mode is applied during a charge mode in consideration of fuel efficiency, and the high mode is applied during a typical charge mode.
In this case, durability of the auxiliary battery and fuel efficiency of the vehicle may be poor since a fixed step voltage unrelated to characteristics of the battery is applied to the battery when a variable control mode of the auxiliary battery is performed. As a result, the battery is charged under a current region of low efficiency for a certain time. In other words, structural merits of the eco-friendly vehicle, load characteristics of the battery, and/or states of the battery are not considered in performing continuous charge of current during transition between the modes or during charge in the same mode.
One measure to solve these problems is disclosed in the document of Korean Patent Laid-Open Publication No. 10-2013-0082360. In the above document, an output voltage of a low voltage converter is variably controlled using state information of a low voltage battery sensed by a low voltage battery sensor and using information of a driven load sensed by a current sensor.
However, in the document, structural merits of the eco-friendly vehicle, load characteristics of the battery, and/or states of the battery are not considered because of using a voltage control mode.